[choidanny719]

Check recording mixes health updates, incident handling, and history cleanup in one transaction callback. JSON expectation validation also puts its shape, path, and value rules into a single long condition.

This refactor:

• Moves health updates and history cleanup into private Store helpers while preserving the existing transaction boundary.
• Separates JSON path and value checks from monitor configuration validation, preserving accepted inputs and error messages.
• Adds regression coverage for incident-write rollback, per-monitor retention, and JSON expectation boundaries.

README, endpoints, features, schema, dependencies, and configuration defaults are unchanged. The changes are split into two commits by area.

Validation: all 28 tests pass with npm test, npm run demo passes, and git diff --check is clean. The new regression cases also passed against the original implementation before each refactor.